Breast cancer is a major cause of mortality in women. One of the factors that influence the chances of curing a patient having breast cancer is early detection of the disease. The major methods for detecting breast cancer currently in use are X-ray mammography imaging and ultrasound imaging. In detecting breast cancer, an image of the breast is generated, using one of these imaging modalities, and a physician inspects the image to determine whether the image is indicative of breast cancer. Such inspection of images requires image analysis specialization from the physician, which adds to the cost of the cancer detecting procedure and/or limits the availability of the procedure to relatively large medical centers. Therefore, in general, only women in high risk groups of breast cancer undergo tests for early detection of breast cancer. These risk groups include, for example, women above the age of about 45 and women having a family history of breast cancer. Generally, different countries set different ages in which X-ray mammography screening is recommended. The chances that a woman in a risk group has cancer is usually much less than 10% and therefore even many women in the risk groups do not go for regular breast cancer detection procedures as recommended.
For women not in a high risk group, for example in the age group of 25-45, there are very low chances, in accordance with current practice, that their cancer will be detected at an early stage. These women, however, have a chance of about 3 to 1000 of having breast cancer, which may not be detected until the cancer is in advanced stages. Women's physicians and aware women perform palpation tests in search for cancer and woman who have suspected lumps detected in their breasts by palpitation are sent for further screening by ultrasound and/or mammography and/or biopsy. However, due to the low risk within the general population, mammography and/or ultrasound are not indicated as screening tools for the general asymptomatic population.
U.S. Pat. No. 5,800,350, to Coppleson et al., the disclosure of which is incorporated herein by reference, describes a probe adapted to apply a plurality of stimuli to a suspected tissue. According to detected responses to the stimuli, the probe provides an indication of the surface tissue type (e.g., normal, pre-cancerous/cancerous, unknown) of the suspected tissue. The probe of U.S. Pat. No. 5,800,350 is not suitable for use with the breast, as cancerous cells in the breast are not generally on the surface of the breast.
An article titled “Breast Electrical Impedance and Estrogen Use in Postmenopausal Women”, G. Piperno, S. Lenington, Mauturitas 41 (2002), the disclosure of which is incorporated herein by reference, describes a clinical test which suggests a correlation between electrical measurements on the nipple and estrogen activity in breast tissue.
U.S. Pat. No. 6,122,544 to Organ, the disclosure of which is incorporated herein by reference, describes a method of identifying cancer by comparing maps of electrical impedance measurements of the breasts. The impedance maps (in the form of matrices) of both breasts of the patient are compared and if a substantial difference is found, cancer is diagnosed in the breast with the higher impedance. U.S. patent publication 2002/0123694 to Organ et al., the disclosure of which is incorporated herein by reference, uses a greater number of electrodes and attempts to localize the lesion, according to a region of the map having a different impedance.
U.S. Pat. No. 5,415,164 to Faupel, the disclosure of which is incorporated herein by reference, describes a self-test method for a breast screening system based on measurement of passive DC signals from the breast. As DC signals require long settling times (due to polarization) before measurements may be acquired, the method includes determining whether the measured signals are stable before measurement of the DC signals for breast screening is allowed, so that it is not required to wait long periods of time when it is not necessary. Such stabilizing waiting periods are characteristic of DC measurements, especially in polarizable materials.
U.S. Pat. No. 6,167,300 to Cherepenin, the disclosure of which is incorporated herein by reference, describes an electric mammography system for obtaining three dimensional images of the breast. The system uses a large surface probe, which may include elements that do not contact the examined breast. These elements are detected according to the values they sense and are excluded from the reconstruction of the three dimensional image.
U.S. Pat. No. 6,026,323 to Skaldnev, the disclosure of which is incorporated herein by reference, describes a probe for characterizing tissue type, for example for breast cancer examination. The probe checks for poor contact due to reasons such as the probe being in an angle to the cervix.
The use of impedance measurements in screening has been mooted by several authors. However, no such screening method has ever been shown to be feasible. In particular, screening requires both high specificity and high sensitivity. In general, it was believed that in the absence of both high sensitivity and specificity, if screening was performed on a general population in which the probability of cancer of the breast is low, either large numbers of women would be subjected to unnecessary additional tests or many woman with cancer would be diagnosed as being free of cancer. It should be noted that mammography, which is used for testing high risk groups has a high sensitivity but a low specificity as do other modalities used to “screen” suspect patients.